For example, in the processes of manufacturing a NAND flush memory or a MRAM (magneto-resistive random-access memory), processes of forming insulator films such as aluminum oxide films, magnesium oxide films, and the like are carried out. Sputtering apparatus is used in order to form insulator films with good productivity. In this kind of sputtering apparatus, a target assembly is assembled, in a detachable manner, onto a vacuum chamber which is capable of being evacuated, the target assembly having integrated together: a target appropriately selected depending on the composition of the thin film to be formed; and a backing plate for cooling the target at the time of film forming by sputtering.
This kind of target assembly is known, e.g., in Patent Document 1. According to this arrangement, the backing plate is formed of metal such as copper with good thermal conduction, and has a projected portion projected outward beyond an outer peripheral end of the target. By taking advantage of this projected portion, it is so arranged that the target assembly can be fixed to a predetermined position of the sputtering apparatus. Further, after having assembled the target assembly onto the sputtering apparatus, an annular shield plate is generally disposed opposite to the projected portion, for the purpose of stabilizing the discharging, etc.
By the way, in a state in which the target assembly and the shield plate have been assembled onto the sputtering apparatus, there is a clearance between the target and the shield plate. When plasma is caused to be generated in the vacuum chamber at the time of film forming, the electrons in the plasma will sometimes be electrostatically charged, through the above-mentioned clearance, in the projected portion that is made of metal. When the projected portion gets charged with electrons, due to the fact that the target is made of an insulating material, abnormal discharging occurs due to the potential difference between the side surface of this target and the projected portion. Due to this phenomenon, there is a case in which the bonding material gets seeped to the outside. If film forming is performed in this kind of state, there will occur so-called contamination in which metal gets mixed into the insulation film that is formed on the surface of a substrate. This will prevent good film formation. As a solution, in order not to expose that bonded surface between the target and the backing plate in which the bonding material exists, it is considered to form a film made of an insulating material (hereinafter called an “insulator film”) so as to bridge over the side surface of the target to the projected portion. However, since the target of an insulating material is manufactured by sintering, its outside surface is smooth. Therefore, even if the insulator film is formed, e.g., by spray coating, and the like, the adhesive force of the film is extremely weak, thereby giving rise to the problem in that the insulator film will easily be peeled off.